docs: def starting(self, start, predicate=None, index=None):
          """
          Retrieves a set of Match objects that starts at given index.
          :param start: the starting index
          :type start: int
          :param predicate:
          :type predicate:
          :param index:
          :type index: int
          :return: set of matches
          :rtype: set[Match]
          """
          return filter_index(_BaseMatches._base(self._start_dict[start]), predicate, index)